This invention is related to a fuel nozzle for a gas turbine engine. In particular, it deals with a fuel nozzle capable of supplying alternately or simultaneously two different types of fuel, such as liquid or gaseous fuel.
A gas turbine engine depends upon the expansion of a burning fuel to drive the turbine wheel of a gasifier turbine. A gasifier turbine drives a compressor which pressurizes air for mixture with fuel for subsequent burning. Once the expanding burning gas has passed the gasifier turbine stage, power may then be extracted to drive either a power turbine or, in the case of an aircraft, act upon the turbine case in the manner of a jet engine.
The combustion chamber or chambers are generally between the compressor and the gasifier turbine, and are formed either as an annular single chamber, or a plurality of cylindrical chambers circumferentially spaced about the turbine shaft. The burning and expanding fuel is directed by a series of nozzle vanes against the blades of the turbine wheel.
Fuel is communicated to the combustion chamber, or combustion chambers in the case of the cylindrical chambers, through a series of fuel nozzles. In an annular chamber, a plurality of fuel nozzles are circumferentially spaced about the engine each leading into the combustion chamber upstream of the turbine wheel. Fuel is communicated through these nozzles to the combustion chamber for burning therein.
A selected number of the fuel injectors may have fixed in their immediate vicinity a means of ignition generally in the form of a sparking plug. The ignitor is energized upon the turbine reaching a particular speed under the influence of an outside power source. Simultaneously, with the excitation of the ignitor or at a predetermined time thereafter, fuel is communicated to the fuel nozzles where it is ignited due to the high temperature in the immediate vicinity resulting from the ignition source.
It is well known in the art that certain fuels ignite more readily than others. In particular, gaseous fuels or atomized fuels properly mixed with air, are usually more easily ignited than a stream of liquid fuel. Thus, it follows that gas turbine engines may be more rapidly started through the use of gaseous or atomized fuel. On the other hand, the less volatile fuels may be appropriate for use once the engine has been started simply from an economic standpoint. Being able to start on one fuel and operate on another is useful, but the ability to change from one fuel to another without interrupting engine operation is equally important.
The high temperatures associated with a gas turbine engine present unique problems in fuel delivery. In particular, the fuel which is usually at the ambient temperature of the environment is delivered to a combustion chamber which is operating at a high temperature. Therefore, the conduit, or passage, communicating the fuel to the combustion chamber is hot at one end and relatively cool at the other end. If the combustion chamber is fixed at one end to the turbine case, the chamber, because of the heat, will expand linearly relative to the surrounding engine case in which the turbine case is mounted. This expansion and any expansion in the passage communicating the fuel to the combustion chamber from the outside of the engine case, must therefore be absorbed in the passage. In fuel nozzles communicating a single fuel to a combustion chamber, the expansion problem may be taken care of by a means well known in the art such as helical coil in the fuel line.
Ideally, fuel should be communicated to a particular point in the combustion chamber to provide optimum burning, and thus optimum power extraction from the burning fuel. Therefore, if more than one type of fuel is utilized in operation of the engine, fuel must be provided through the same nozzle or replacement nozzles, and may require shutting the engine down to effect fuel change. Provision in the present gas turbine engines for multiple fuel use is generally done through a valving scheme so that a first fuel is communicated to the nozzle through one conduit, while a second fuel is communicated to the same nozzle through a second conduit. This may prevent continuous operation of the engine during fuel shiftover. Since repeated starting of a gas turbine engine in a hot condition may not always be desirable, shut down of the engine for shiftover to a second type of fuel should be avoided, if possible. Since it is advantageous to be able to utilize various types of fuel in an operating gas turbine and further since it may be advantageous to shift from one type of fuel to a second type of fuel during operation, it became apparent that the existing fuel nozzles are inadequate.